Cryoablation therapy is a technique that uses freezing to locally destroy or alter body tissue, such as a tumor, cardiac tissue associated with arrhythmia, or diseased or congenitally abnormal tissue. Surgical cryoprobes and cryoablation catheters are typically used to perform this technique, and may generally include a power source, a coolant source, and one or more treatment elements. Commonly used cryoablation treatment elements include expandable elements (for example, balloons) through which cryogenic fluid, such as a phase-change coolant, circulates. The temperature of phase-change coolants is lowered via the Joule-Thomson effect, which occurs when the coolant expands within the treatment element.
When the treatment elements of the catheter must chill tissue to below freezing, the coolant itself must attain a substantially lower temperature. Although phase-change coolants can reach sufficient temperatures at expansion, coolant temperature rapidly rises after expansion within the treatment element. For example, a small coolant-filled balloon must overcome the heat of blood flow and surrounding tissue to maintain freezing temperatures. Typically, this problem is solved by injecting coolant into the treatment element at high flow rates and pressures, with rapid removal and replacement with fresh coolant. However, conditions of patient safety must be considered. When high pressures are be required to circulate sufficient coolant through the catheter body to its tip and back, and the overall design of a catheter must be such that fracture of the catheter or leakage of the coolant either does not occur, or if it occurs, is harmless. Further, for an endovascular catheter construction, the presence of the coolant and circulation system should not substantially impair the flexibility or maneuverability of the catheter tip and body.
Patient safety must also be considered when choosing the shape of the cryoablation treatment element. For example, a balloon catheter should be sized and shaped to adequately occlude an area of the body such as the pulmonary vein. However, ablating tissue with a balloon shape that is optimal for occlusion, such as a teardrop shape, may increase the risk of the balloon getting deep in the vein and leading to pulmonary vein stenosis or other vascular damage. Additionally in order to apply a spherical balloon ‘head-on’ against a flat structure like the posterior wall, the distal “neck” of the balloon will need to be withdrawn sufficiently to allow contact by the rest of the balloon.
Accordingly, it would be desirable to provide a cryoablation device and system that would more efficiently circulate coolant through the treatment element proximate the target tissue without necessitating potentially dangerous high pressures and flow rates. Additionally, it would be desirable if this cryoablation device and system further included the ability to change the shape of the treatment element to enable a single device to serve multiple purposes.